Overspeed control for turbine rotor



Dec. 27, 1960 H. GARDNER OVERSPEED CONTROL FOR TURBINE ROTOR 2Sheets-Sheet 1 Filed June 20, 1.957

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INVENTOR HORACE L.GARDNER IS ATTORNEYS Dec. 27, 1960 H. GARDNEROVERSPEED CONTROL FOR TURBINE ROTOR 2 Sheets-Sheet 2 Filed June 20. 1957FIG.6.

INVENTOR HORACE L.GARDNER HISATTORNEYS United States Patent OVERSPEEDCONTROL FOR TURBINE ROTOR Horace L. Gardner, Islip, N.Y., assignor toFairchild Engine and Airplane Corporation, Hagerstown, Md., acorporation of Maryland Filed June 20, 1957, Ser. No. 666,937

3 Claims. (Cl. 253-59) This invention relates to an overspeed controlfor a turbine rotor in which, in the event of overspeed operation of theturbine rotor, the effective area of the inlet passage or passagesthrough which the impelling fluid is directed toward the turbine rotoris substantially reduced, thereby substantially reducing the rotorspeed.

It is well known that runaway turbines are highly dangerous due to thepossibility of failure of the turbine rotor. Because of the extremelyhigh rotational speeds at which turbine failures occur, it is notunusual for large fragments of the rotor to be projected with sufficientforce to penetrate the housing within which the rotor is situated. It isapparent that such failures present an extreme hazard to both personneland equipment.

In many conventional turbines the impelling fluid is directed againstthe turbine rotor through passages formed between a plurality of statorvanes. The stator vanes are ordinarily arranged in a circular array,either laterally offset from the impeller blades carried by the turbinerotor or around the outer periphery of the turbine blades carried by therotor. In either case their function is to direct the impelling fluid inthe desired direction against the impeller blades of the turbine rotor.

In the overspeed control of the present invention, the stator vanes aresplit into upstream and downstream portions, and the upstream anddownstream portions are so mounted that they can be moved relatively toeach other to decrease the effective area of the passages through whichthe impelling fluid is directed against the turbine rotor. This decreasein area, in turn, reduces the energy which the impelling fluid transmitsto the turbine rotor, and so has the effect of slowing down the turbinerotor.

For a complete understanding of the present invention, reference may behad to the detailed description which follows and to the accompanyingdrawings in which:

Figure 1 is a fragmentary cross-sectional view of a portion of a turbineembodying the present invention;

Figure 2 is a cross-sectional view, taken along the line 2-2 of Figure1, looking in the direction of the arrows;

Figure 3 is a view similar to Figure 2 but illustrating the relativedisplacement between the upstream and downstream portions of the statorvanes in the event of overspeed operation of the turbine rotor;

Figures 4 and 5 are fragmentary views, partly in crosssection, takenalong the lines 4-4 and 55, respectively, of Figure 1, looking in thedirection of the arrows; and

Figure 6 is a view similar to Figure 1, but illustrating anotherembodiment of the invention.

Referring to the drawings, a turbine rotor 10 is mounted on a rotatableshaft 11 within a turbine housing 12. The turbine illustrated in thedrawings is an axial flow type wherein an impelling fluid is directedunder pressure through a passage 13 toward the impeller blades 14affixed to the outer periphery of the rotor 10. The annular passage 13is defined between the inner surface of the housing 12 and the outersurface of a cylindrical support member 15 mounted centrally within theupstream end of the housing 12. As shown in Figure 5, the end of the2,966,332 Patented Dec. 27, 1960 support member serves as a bearing forthe rotatable shaft 11. A plurality of stator vanes, generallydesignated 16, are mounted within the annular passage 13 to direct theimpelling fluid in the desired direction against the impeller blades 14of the turbine rotor.

In accordance with the present invention, the stator vanes 16 are eachsplit so as to form an upstream component 16a and a downstream component16b. The upstream components 16a of the stator vanes are mounted aroundthe outer periphery of a common annular support member 18 which isaffixed to the end of the support member 15 by means of screws 19. Thedownstream components 16b of the stator vanes are aflixed to the outerperiphery of a common annular support member 20 which is rotatablymounted with respect to the support member 18 from the positionillustrated in Figure 2 to the position illustrated in Figure 3. Morespecifically, the support member 20 is held by a plurality of screws 21to the adjacent face of the support member 18. The screws 21 passthrough arcuate slots 23 in the support member 20, permitting limitedrotational movement of the support member 20 relative to the supportmember 18. The screws 21 carry compressed springs 24 thereon which exertpressure against a face of the support member 20, urging the oppositeface thereof against the adjacent face of the support member 18. Thepressure exerted by the springs can be adjusted by tightening orloosening the screws, and in this way the frictional resistance of thesupport member 20 to rotate relatively to the support member 18 can beregulated. The opposed faces of the support members 18 and 20 arealigned with respect to each other by a tongue and slot engagement. Morespecifically, referring to Figure 1, the lateral face of the supportmember 20 is provided with a curved tongue 25 which is accommodatedwithin a curved slot 26 formed in the opposite face of the supportmember 18.

In the normal operation of the turbine rotor, the downstream components16b of the stator vanes are registered with respect to the upstreamcomponents 16a thereof, as shown in Figure 2, so that the passages aintermediate adjacent downstream components 16b are substantiallycontinuous with the passages b intermediate the upstream components 16aof the stator vanes. In the event of overspeed operation of the turbinerotor, however, the support member 20 is adapted to be rotatedrelatively to the support member 18 to a position in which thedownstream components 16b are offset with respect to the upstreamcomponents 16a of the stator vanes. In the position illustrated inFigure 3, the downstream components 16b of the stator blades are movedinto substantial registry with the passages b between upstreamcomponents of the stator vanes, and the upstream components 16a are insubstantial registry with the passages a between the downstreamcomponents of the stator vanes. This represents a displacement of thesupport member 20 equal to one-half of the spacing between the upstreamcomponents of the stator vanes. As a result, the effectivecross-sectional area of the passages intermediate the stator vanes issubstantially reduced along the plane formed by the abutting faces ofthe support members 18 and 20. This reduction in effectivecross-sectional area acts as a valve to reduce the flow of impellingfluid against the impeller blades 14 of the turbine rotor and, hence,substantially reduces the speed at which the turbine rotor is driven bythe impelling fluid.

Provision is made in the present invention for automatically displacingthe support members 18 and 20 relative to each other in the event of anoverspeed operation of the turbine rotor. To accomplish this a pluralityof trip flanges or projections 28 are mounted in circular array to theface of the turbine rotor 10 adjacent the support member 20, and aplurality of radial pins 29 are mounted to the support member 20 incircular array just outboard of the outer periphery of the projections28. In the event of an overspeed operation of the turbine rotor,centrifugal force will deflect the trip projections outwardly, so thatthe outer surface of one or more of the trip projections willfrictionally engage the inner end of one or more of the pins 29. Thisfrictional engagement between the projections 28 and the pins 29 willrotatably displace the support member 20 relatively to the supportmember 18, at least to the extent permitted by the length of the arcuateslots 23 in the support member 20, thereby moving the support member 20to the position illustrated in Figure 3. The resulting decrease in thecross-sectional area of the passages between the stator blades resultsin a decrease in the speed of rotation of the turbine rotor.

The trip projections 28 are illustrated in Figure 4 as elongatedprojections of arcuate curvature, but shorter or longer trip projectionsmay be used. Preferably, however, the length of the trip projections 28is designed to exceed the space between adjacent pins 29. In this way,the outer surface of the trip projection 28 will engage the inner end ofa pin 29 and displace the support member 20 without damage to either theprojection or the pin. n the other hand, the trip projections may bemade shorter in length, in which case they will be more readilydeflected outwardly by centrifugal force. If so designed, the leadingedge of a trip projection may serve to engage one of the pins 29 and sodisplace the support member 20 from the position shown in Figure 2 tothe position shown in Figure 3. Of course, in this case either theprojection or pin will be sheared off. The slight damage caused byshearing off the pin or trip projection, however, is incidental incomparison with the very severe damage which is possible if the speed ofthe turbine rotor is not checked.

A modified form of the invention is illustrated in Figure 6 of thedrawings. In this embodiment, the turbine rotor 30 carrying impellerblades 31 around the outer periphery thereof is mounted within a turbinehousing 32. As in the form of the invention described above, theimpelling fluid flowing through the passage 33 is guided by split statorvanes, generally designated 34, against the impeller blades 31, therebydriving the turbine rotor 30. The upstream components 34a of the splitstator vanes are mounted around the outer periphery of an annularsupport member 35, and the downstream components 34b of the statorblades are mounted around the outer periphery of an annular supportmember 36. The annular support member 35, as in the form of theinvention illustrated in Figures 1 to of the invention, is anchored byscrews 37 to the frame structure 32a. The support member 36, in turn, isaffixed to the support member 35 by screws 38 which pass through arcuateslots 39 in the support member 36 to permit displacement of the member36 relative to the support member 35 in the event of overspeed operationof the turbine rotor. Spring washers 40 carried by the screws 38 servethe function of the compression springs 24 in the form of the inventiondescribed above.

In this form of the invention, the shear pins 42 interposed in alignedholes of the support members 35 and 36 determine the registered positionof the blade components 34a and 34b. In the event of an overspeedoperation of the turbine rotor, the pins 42 are readily sheared,permittin the displacement of the downstream components 34b of thestator blades relative to the upstream components 341: thereof.

In this modification, an extended shroud 45 encircles both thedownstream components 34b of the stator vanes and the turbine rotor. Theannular shroud 45 is attached to the outer peripheries of the downstreamcomponents 34b of the statorvanes, but there is a small clearanceprovided between the outer edges of the impeller blades 31 and the innerperiphery of the annular shroud 45.

It is a well known phenomenon that turbine rotors rotating at highspeeds expand in diameter, principally due to the effect of centrifugalforce. The expansion of the turbine rotor at high speeds is utilized inthis modification of the invention to displace the downstream statorcomponents 34b relatively to the upstream components 34b thereof in theevent of overspeed operation of the turbine rotor. More specifically, inthe event of overspeed rotation of the turbine rotor, the outer edges ofthe impeller blades 41 will contact the inner surface of the annularshroud 45, and the frictional engagement therebetween will shear thepins 42 and displace the stator components 341) relatively to thecomponents 34a to the extent permitted by the length of the arcuate slot39. This permits the stator components 34b to rotate a distance equal toone-half the spacing between the upstream components 34a of the statorvanes, thereby appreciably reducing the effective area of the passage 33to the impeller blades 31.

The invention has been shown and described in pre ferred forms and byway of example only, and obviously many modifications and variations maybe made in the invention without departing from the spirit thereof. Theinvention, therefore, is not to be limited to any specified form orembodiment, except in so far as such limitations are set forth in theclaims.

I claim:

1. An overspeed control for a turbine rotor which carries a plurality ofimpeller blades mounted in a circular array comprising a housing,passage in the housing for conducting an impel-ling fluid to theimpeller blades of the turbine rotor, a plurality of stator vanesarranged in the passage immediately upstream of the impeller blades fordeflecting the impelling fluid and directing it against the faces of theimpeller blades, said stator vanes being split into upstream anddownstream components, the downstream components of the stator bladesconstituting one group and the upstream components of the stator vanesconstituting another group, a common movable support for the componentsof one of the groups, an independent support for the components of theother of said groups, means for limiting the relative displacementbetween the supports from one extreme position in which the upstream anddownstream components of the stator vanes are aligned in complementaryfashion to another extreme position in which the upstream and downstreamcomponents of the stator vanes are out of alignment so as to cut downthe rate of flow of the impelling fluid to the impeller blades, meansfor yieldingly locking the supports irrespective of which of saidextreme relative positions the two supports are positioned, the twosupports being arranged so as to position the upstream and downstreamcomponents of the stator vanes in alignment at all speeds below apredetermined speed within the safe range, an inner deflectible elementcarried by the turbine rotor, an outer cooperating element carried bythe movable support, the deflectible element carried by the turbinerotor being translated thereby at safe speeds of operation below thepredetermined speed in a circular path closer to the axis of rotation ofthe rotor than the outer cooperating element and out of contacttherewith, the centrifugal force at higher speeds causing thedeflectible element to move outwardly from the axis of rotation of therotor and into engagement with the cooperating element carried by themovable support, the engagement therebetween imparting rotation to themovable support to shift the movable support from the extreme positionof alignment between the upstream and downstream components of thestator vanes to the other extreme position of misalignment therebetween.

2. An overspeed control for a turbine rotor as set forth in claim 1 inwhich the means for yieldingly locking the supports comprises acompressed spring which acts against one face of the movable support andincluding spring retaining means connected to the independent supportfor maintaining the compressed spring in position to exert a forceagainst the said movable support in order to yieldingly lock the twosupports in either of said extreme relative positions.

3. An overspeed control for a turbine as set forth in claim 2 in whichthe movable support and the independent support are in face-to-facerelationship and including means defining an aperture in the movablesupport to accommodate the spring retaining element, whereby the springacts to yieldingly lock the supports by increasing the frictionalcontact therebetween.

References Cited in the file of this patent UNITED STATES PATENTSPollard et al. Ian. 10, Entz Dec. 31, Graham et al. Jan. 18, Millns Oct.2, Teague Oct. 7, Volk Sept. 8, Iaquith Jan. 19,

FOREIGN PATENTS Canada Mar. 8, France June 22,

